1. Field
The disclosed embodiments relate to a method for bonding two metal surfaces, a method for producing an object preferably having cavities therein, an object having cavities, and a structure of a light emitting diode.
2. Brief Description of Related Developments
A typical field of use of the aspects of the disclosed embodiments is the production of small, flat, but complex-shaped cooling elements having a supply opening and a drain opening for a cooling fluid and having fluid channels formed in the cooling element. Such cooling elements can, e.g., be used for small semiconductors, such as semiconductor laser diodes.
The basic method serves for bonding two partially form-fitting surfaces of two metal bodies which comprise the same material or consist of the same material/metal. The bodies can be flat bodies, such as thin sheet metal or foils. They can be structured, then superposed on each other and, subsequently, bonded to each other, so that in the interior the desired structures are formed according to the structuring of the individual bodies/sheets/foils.
FIG. 6 exemplarily shows the underlying technology. There are provided several bodies 10a, 10b, 10c and 10d which can be structured individually. Reference numerals 61, 62, 63, 64, 65 and 69 denote cut-outs of the otherwise provided plain of the body. The bodies 10 are metal sheets or foils, e.g. sheet copper, of a thickness (in FIG. 6 in z-direction, perpendicularly to the plane of projection) of preferably below 2 mm, further preferably below 1 mm, further preferably below 0.5 mm. After their making, e.g. in the shapes as shown in FIG. 6, the metal sheets are superposed on each other in a way still to be described and are bonded to each other in a fluid-tight manner, so that within the object cavities corresponding to the recesses in the individual bodies are formed.
In the shown example, 10a designates the uppermost body of the stack to be formed. The holes 69 do not have any relation to the cavities to be formed in the object. They are rather alignment structures which facilitate the precise superposition of the individual bodies 10. 61 and 62 are openings, wherein, e.g., 61 may be a supply for a fluid and 62 a drain for the fluid. 10b is the second body lying beneath the first body. It shows a horseshoe-shaped channel 63 which is positioned and designed in such a way that its above horizontally located leg is in fluid communication with the schematically shown supply opening 61 of the body 10a. According to the directions of the arrows the fluid can flow downwards in the drawing plane to the areas 64 which are in fluid communication with the areas 64 in the third body 10c lying farther below. The body 10b also shows an opening 62 which is in fluid communication with the opening 62 in the body 10a and through-connects the same “downwards”. The body 10c shows a recess 65 according to an upside-down T. From the areas 64 the fluid can flow upwards in the drawing plane up to the area 62 which, in its spatial position, corresponds to the areas 62 in the bodies 10b and 10a, so that the fluid can flow off again via this connection. The body 10d finally is a lid which seals off the cooling element against beneath.
In the z-direction the overall structure can have a thickness of few millimeters. The structure can be more complex than that in the example of FIG. 6. If the thickness of a body 10a in z-direction is, e.g., 0.3 mm and 8 layers are superimposed to each other, an overall structure having a thickness of about 2.4 mm is formed.
When bonding the individual bodies 10 this must be effected in such a way that the bond is fluid-tight all around and unsusceptible towards temperature variations and influences of the flowing fluid.
The bodies 10 can comprise copper or can consist thereof to a large proportion.
For bonding the bodies a method being termed “direct copper bonding” has been known. In this method the surfaces of the copper plates to be bonded to each other are coated with a eutectic mixture of copper and copper oxide (Cu2O and CuO) of a specific thickness. Then, the surfaces coated in such a way are placed adjacent to each other and heated to a temperature between the melting point of pure copper (about 1083° C.) and the melting point of the above-mentioned eutectic (about 1063° C.), e.g. to about 1070° C. Caused by the heating the eutectic melts and the subsequent solidification leads to a connection of the surfaces.
The disadvantage of this known method is that Cu2O as well as CuO are thermally instable and, therefore, tend to decompose during the heating process up to the above-mentioned temperature, so that, when the target temperature has been reached, the conditions regarding the eutectic are no longer as they were desired, so that the bonding process would be unsatisfactory without further stabilizing measures. In order to obtain satisfying results, during the heating process a suitable partial pressure of oxygen must be set, and/or additional oxidizing agents must be used, e.g. manganese dioxide. The control of the partial pressure of oxygen is, however, complex, and the use of manganese dioxide leads to further undesired decomposition products and to instabilities of the produced object.
Further known techniques in the relevant field can be inferred from DE 3930859 C2, DE 102004012232 A1, DE 19956565 B4 and from DE 102004002841 B3.